Novel Acoustic Damping Materials

The concept basic to the new smart or intelligent materials is that sensors and actuators of various types can be incorporated in or attached to plates, beams, shells and similar structural members and provide either information on the integrity of the component in its service environment or through some external activation modify the properties of the member in some beneficial manner. In the former mode of operation, the sensor might be a piezoelectric or shape memory element or a fiber optic device which would provide early detection of a fatigue derived defect or the onset of some structural change which could ultimately impair the performance of the structure. Used as an active element in the structure the modal response, acoustic radiation or transmission can be modified as well as the internal damping or suppression of vibration. The major attention being given to this new class of material is in the field of composites where the opportunity to design into the structure a wide variety of properties is possible. At the present time emphasis has been on fiber reinforced plastics such as glass-epoxy and graphite- epoxy composites which are broadly used in aircraft and aerospace structures.